package io.polaris.core.codec;

import java.io.IOException;
import java.io.OutputStream;

/**
 * @author Qt
 * @since 1.8
 */
public class Base64Encoder implements Encoder {
	protected final byte[] encodingTable =
		{
			(byte) 'A', (byte) 'B', (byte) 'C', (byte) 'D', (byte) 'E', (byte) 'F', (byte) 'G',
			(byte) 'H', (byte) 'I', (byte) 'J', (byte) 'K', (byte) 'L', (byte) 'M', (byte) 'N',
			(byte) 'O', (byte) 'P', (byte) 'Q', (byte) 'R', (byte) 'S', (byte) 'T', (byte) 'U',
			(byte) 'V', (byte) 'W', (byte) 'X', (byte) 'Y', (byte) 'Z',
			(byte) 'a', (byte) 'b', (byte) 'c', (byte) 'd', (byte) 'e', (byte) 'f', (byte) 'g',
			(byte) 'h', (byte) 'i', (byte) 'j', (byte) 'k', (byte) 'l', (byte) 'm', (byte) 'n',
			(byte) 'o', (byte) 'p', (byte) 'q', (byte) 'r', (byte) 's', (byte) 't', (byte) 'u',
			(byte) 'v',
			(byte) 'w', (byte) 'x', (byte) 'y', (byte) 'z',
			(byte) '0', (byte) '1', (byte) '2', (byte) '3', (byte) '4', (byte) '5', (byte) '6',
			(byte) '7', (byte) '8', (byte) '9',
			(byte) '+', (byte) '/'
		};

	protected byte padding = (byte) '=';

	/*
	 * set up the decoding table.
	 */
	protected final byte[] decodingTable = new byte[128];

	protected void initialiseDecodingTable() {
		for (int i = 0; i < decodingTable.length; i++) {
			decodingTable[i] = (byte) 0xff;
		}

		for (int i = 0; i < encodingTable.length; i++) {
			decodingTable[encodingTable[i]] = (byte) i;
		}
	}

	public Base64Encoder() {
		initialiseDecodingTable();
	}

	public int encode(byte[] inBuf, int inOff, int inLen, byte[] outBuf, int outOff) throws IOException {
		int inPos = inOff;
		int inEnd = inOff + inLen - 2;
		int outPos = outOff;

		while (inPos < inEnd) {
			int a1 = inBuf[inPos++];
			int a2 = inBuf[inPos++] & 0xFF;
			int a3 = inBuf[inPos++] & 0xFF;

			outBuf[outPos++] = encodingTable[(a1 >>> 2) & 0x3F];
			outBuf[outPos++] = encodingTable[((a1 << 4) | (a2 >>> 4)) & 0x3F];
			outBuf[outPos++] = encodingTable[((a2 << 2) | (a3 >>> 6)) & 0x3F];
			outBuf[outPos++] = encodingTable[a3 & 0x3F];
		}

		switch (inLen - (inPos - inOff)) {
			case 1: {
				int a1 = inBuf[inPos++] & 0xFF;

				outBuf[outPos++] = encodingTable[(a1 >>> 2) & 0x3F];
				outBuf[outPos++] = encodingTable[(a1 << 4) & 0x3F];
				outBuf[outPos++] = padding;
				outBuf[outPos++] = padding;
				break;
			}
			case 2: {
				int a1 = inBuf[inPos++] & 0xFF;
				int a2 = inBuf[inPos++] & 0xFF;

				outBuf[outPos++] = encodingTable[(a1 >>> 2) & 0x3F];
				outBuf[outPos++] = encodingTable[((a1 << 4) | (a2 >>> 4)) & 0x3F];
				outBuf[outPos++] = encodingTable[(a2 << 2) & 0x3F];
				outBuf[outPos++] = padding;
				break;
			}
		}

		return outPos - outOff;
	}

	@Override
	public int getEncodedLength(int inputLength) {
		return (inputLength + 2) / 3 * 4;
	}

	@Override
	public int getMaxDecodedLength(int inputLength) {
		return inputLength / 4 * 3;
	}

	/**
	 * encode the input data producing a base 64 output stream.
	 *
	 * @return the number of bytes produced.
	 */
	@Override
	public int encode(byte[] buf, int off, int len, OutputStream out)
		throws IOException {
		if (len < 0) {
			return 0;
		}

		byte[] tmp = new byte[72];
		int remaining = len;
		while (remaining > 0) {
			int inLen = Math.min(54, remaining);
			int outLen = encode(buf, off, inLen, tmp, 0);
			out.write(tmp, 0, outLen);
			off += inLen;
			remaining -= inLen;
		}
		return (len + 2) / 3 * 4;
	}

	private boolean ignore(
		char c) {
		return (c == '\n' || c == '\r' || c == '\t' || c == ' ');
	}

	/**
	 * decode the base 64 encoded byte data writing it to the given output stream,
	 * whitespace characters will be ignored.
	 *
	 * @return the number of bytes produced.
	 */
	@Override
	public int decode(
		byte[] data,
		int off,
		int length,
		OutputStream out)
		throws IOException {
		byte b1, b2, b3, b4;
		byte[] outBuffer = new byte[54];   // S/MIME standard
		int bufOff = 0;
		int outLen = 0;

		int end = off + length;

		while (end > off) {
			if (!ignore((char) data[end - 1])) {
				break;
			}

			end--;
		}

		// empty data!
		if (end == 0) {
			return 0;
		}

		int i = 0;
		int finish = end;

		while (finish > off && i != 4) {
			if (!ignore((char) data[finish - 1])) {
				i++;
			}

			finish--;
		}

		i = nextI(data, off, finish);

		while (i < finish) {
			b1 = decodingTable[data[i++]];

			i = nextI(data, i, finish);

			b2 = decodingTable[data[i++]];

			i = nextI(data, i, finish);

			b3 = decodingTable[data[i++]];

			i = nextI(data, i, finish);

			b4 = decodingTable[data[i++]];

			if ((b1 | b2 | b3 | b4) < 0) {
				throw new IOException("invalid characters encountered in base64 data");
			}

			outBuffer[bufOff++] = (byte) ((b1 << 2) | (b2 >> 4));
			outBuffer[bufOff++] = (byte) ((b2 << 4) | (b3 >> 2));
			outBuffer[bufOff++] = (byte) ((b3 << 6) | b4);

			if (bufOff == outBuffer.length) {
				out.write(outBuffer);
				bufOff = 0;
			}

			outLen += 3;

			i = nextI(data, i, finish);
		}

		if (bufOff > 0) {
			out.write(outBuffer, 0, bufOff);
		}

		int e0 = nextI(data, i, end);
		int e1 = nextI(data, e0 + 1, end);
		int e2 = nextI(data, e1 + 1, end);
		int e3 = nextI(data, e2 + 1, end);

		outLen += decodeLastBlock(out, (char) data[e0], (char) data[e1], (char) data[e2], (char) data[e3]);

		return outLen;
	}

	private int nextI(byte[] data, int i, int finish) {
		while ((i < finish) && ignore((char) data[i])) {
			i++;
		}
		return i;
	}

	/**
	 * decode the base 64 encoded String data writing it to the given output stream,
	 * whitespace characters will be ignored.
	 *
	 * @return the number of bytes produced.
	 */
	@Override
	public int decode(
		String data,
		OutputStream out)
		throws IOException {
		byte b1, b2, b3, b4;
		byte[] outBuffer = new byte[54];   // S/MIME standard
		int bufOff = 0;
		int length = 0;

		int end = data.length();

		while (end > 0) {
			if (!ignore(data.charAt(end - 1))) {
				break;
			}

			end--;
		}

		// empty data!
		if (end == 0) {
			return 0;
		}

		int i = 0;
		int finish = end;

		while (finish > 0 && i != 4) {
			if (!ignore(data.charAt(finish - 1))) {
				i++;
			}

			finish--;
		}

		i = nextI(data, 0, finish);

		while (i < finish) {
			b1 = decodingTable[data.charAt(i++)];

			i = nextI(data, i, finish);

			b2 = decodingTable[data.charAt(i++)];

			i = nextI(data, i, finish);

			b3 = decodingTable[data.charAt(i++)];

			i = nextI(data, i, finish);

			b4 = decodingTable[data.charAt(i++)];

			if ((b1 | b2 | b3 | b4) < 0) {
				throw new IOException("invalid characters encountered in base64 data");
			}

			outBuffer[bufOff++] = (byte) ((b1 << 2) | (b2 >> 4));
			outBuffer[bufOff++] = (byte) ((b2 << 4) | (b3 >> 2));
			outBuffer[bufOff++] = (byte) ((b3 << 6) | b4);

			length += 3;
			if (bufOff == outBuffer.length) {
				out.write(outBuffer);
				bufOff = 0;
			}

			i = nextI(data, i, finish);
		}

		if (bufOff > 0) {
			out.write(outBuffer, 0, bufOff);
		}

		int e0 = nextI(data, i, end);
		int e1 = nextI(data, e0 + 1, end);
		int e2 = nextI(data, e1 + 1, end);
		int e3 = nextI(data, e2 + 1, end);

		length += decodeLastBlock(out, data.charAt(e0), data.charAt(e1), data.charAt(e2), data.charAt(e3));

		return length;
	}

	private int decodeLastBlock(OutputStream out, char c1, char c2, char c3, char c4)
		throws IOException {
		byte b1, b2, b3, b4;

		if (c3 == padding) {
			if (c4 != padding) {
				throw new IOException("invalid characters encountered at end of base64 data");
			}

			b1 = decodingTable[c1];
			b2 = decodingTable[c2];

			if ((b1 | b2) < 0) {
				throw new IOException("invalid characters encountered at end of base64 data");
			}

			out.write((b1 << 2) | (b2 >> 4));

			return 1;
		} else if (c4 == padding) {
			b1 = decodingTable[c1];
			b2 = decodingTable[c2];
			b3 = decodingTable[c3];

			if ((b1 | b2 | b3) < 0) {
				throw new IOException("invalid characters encountered at end of base64 data");
			}

			out.write((b1 << 2) | (b2 >> 4));
			out.write((b2 << 4) | (b3 >> 2));

			return 2;
		} else {
			b1 = decodingTable[c1];
			b2 = decodingTable[c2];
			b3 = decodingTable[c3];
			b4 = decodingTable[c4];

			if ((b1 | b2 | b3 | b4) < 0) {
				throw new IOException("invalid characters encountered at end of base64 data");
			}

			out.write((b1 << 2) | (b2 >> 4));
			out.write((b2 << 4) | (b3 >> 2));
			out.write((b3 << 6) | b4);

			return 3;
		}
	}

	private int nextI(String data, int i, int finish) {
		while ((i < finish) && ignore(data.charAt(i))) {
			i++;
		}
		return i;
	}
}
